One thing about the vehicle engine driven alternator, the single V belt and serpentine belt can only handle so much alternator load.
My engine has parallel V belts for alternator and AC compressor, but I do not use the AC. Using two v belts, just for the alternator, the second V belt was either too tight or too loose, even when I bought marched belts from the same batch. weird harmonics would develop when one belt started resonating. I now only use one V belt instead, but I only have 90Ah of high$$ AGM capacity, and the belt can only be maxed out for a short while no matter how depleted.
A huge depleted battery bank, and my single V belt would be inadequate in the extreme.
They say One v belt is only good for so much amperage, and this is true, I can get mine to slip at higher rpms and higher loads, especially when wet/damp with a depleted battery and other loads, like the lights and blower motor on highest speed which alone can suck up 35 amps.
Another consideration is the heat the alternator develops. I have found that my alternator maxed out, idling, when the engine is already hot, causes alternator temperature to skyrocket. but the same, or even higher load at highway speed and engine rpm( ~1900) has the alternator temperature at a mere 120F or so and in no danger. but hot idling maxed out the alternator temp will skyrocket from 120F to 160F in 30 seconds. 220F is the danger zone where they wear considerably faster
My temp sensor is epoxied to the alternator casing and would be closest to Stator temperature, not rectifier temperature which is likely hotter has more of an effect on output. So my Data could certainly be more accurate if I moved the sensor to the rectifier.
One can use an external rectifier:
https://alternatorparts.com/quicktifier-external-bridge-rectifier.html
And keep much of the heat from the alternator and increasing its lifespan,and output, although on some marine forums the reported output increase is disappointing.
Another option is dual alternators, perhaps the secondary unit dedicated for house battery. I am not sure how best to combine the outputs of two alternators under one voltage regulator, the issues arising once absorption voltage is reached, which can be quickly with high amperages and not so huge battery capacities.
Here is a link on how I tricked the engine computer voltage regulator and wired up the external adjustable voltage regulator on my 89 dodge.
https://vanlivingforum.com/Thread-Your-Vehicles-voltage-regulator?highlight=voltage+regulator
I will not Idle just to recharge, but I do want the most effective use of my alternator when the engine is running, when I am moving from A to B. Cold idling when first started I max out at 62 amps and am good for about 12 to 15 minutes before stator temps exceed 160F, but amps will have tapered to 46 max by then, at hot idle, and 8.2 amps are going into powering the fuel pump, ignition and alternator field.
The high amps of the alternator does not address the fact that 80% to 100% requires 3.5 hours, minimum, at absorption voltage, so my VR modification, will keep the time to achieve 100% when driving to a minimum, the time to 100% cannot be accomplished in less than 3.5 hours from 80%, no matter what. but 3.5 is so much better than 8 or 10 or 16 which might be the case if the vehicles VR decided 13.6 is not only fine, but dandy as well.
I raise a violent, hate filled middle finger to automatic charging sources determining which is just fine and dandy.
And that 100% recharge is Key not only to maximizing battery longevity and performance, it is also key to keeping that time span from 80 to 100% from increasing from 3.5 hours at best, to 2x that duration when the battery becomes sulfated. When a sulfated battery does not get this extra time at absorption voltage, its usuable capacity just declines that much faster and hail mary attempts to restore capacity require more effeort and the results of extended EQ charges less likely to be successful.
So battery longevity is a trade off, No sense in idling for 4 hours to reach that 100%, when Solar can do the dinal 3.5 hours silently, on a good day. No sense in spending 100$ in fuel to promote battery life by 50$ worth of usage, if one can simply replace quality batteries at their convenience.
Battery longevity is a balanacing act, Reaching true 100% is important, but it need not be accomplished every single recharge cycle, but the more it is, the better. But 100% should be considered mandatory, at least every so many deep cycles, unless one can afford to simply view batteries as disposable. Is 100 deep cycles acceptable on the prroly kept battery, where as the well kept battery can achieve 500 cycles and the very well kept battery can achieve 800 deep cycles?
Many influencing factors to the actual numbers. Lead Acid is User friendly, but for the need to achieve 1005 and the actual time required for it to get to a true 100%, and the fact that this time cannot be reduced. 80% to 100% takes 3.5 hour minimum. gettint to 80% can be accomplished quickly with a high amp charging source.
Your strategy is up to you, but that 100% recharge is a hinge point in battery life, the time to reach 100% is where enough solar wattage really pays for itself, especially when high amp alternator can get the batteries above 80% and the solar can then take over and finish the low amps for 6 hours to near or attain that true 100% state of charge.
Some Might choose to simply kill a battery quickly by improper recharging, and use the warranty to get a new battery..
I equate this as driving a new car into the ocean at low tide, and expecting the dealer to give you a new car soon as you can tow it to the dealer.
I find it so surprising that the car dealer/ battery retailer actually has no choice but to warranty the first murdered battery.
If one decides that usig the main engine and idling to recharge is the course they want to seek, i recommend engineering a cold air intake for the alternator, forcing ambient temperature air against the alternator to keep it cool.
Whether the particular engine enjoys or depises idling for extended times is an unknown variable and platform specific.
Everything is a trade off, Knowing the variables and the results of changing those variables should be quantified to come out with an acceptable result.
Refining the data requires measuring tools to collect the data, experimentation, and the correct mindset to look beyond internet theory and folklore.
This sounds extreme, but having high amperage get the batteries to 80% and then lower amperage sources like Solar to finish off the job where low currents for 4 + hours can complete the task of reaching or simply nearing 100%, can mean the difference in replacing their batteries at 3 months, or three years.
One will often hear of someones system and methods and how it is still going strong, or just fine, but most only know something is wrong when battery capacity has declined to the point it cannot meet their overnight needs, and 'just fine' simply means that day could be tomorrow, but today is still going strong. When just fine, no longer is, seems to shock many with the abruptness at which it occurs.
I love the ideal of a DC generator, and a capable alternator feeding huge amps into a depleted battery bank. but once that bank gets to absorption voltage at high amps, the amount of amps that bank can accept starts declining, and that rate of declines the closer it gets to 100%.
No way around this fact, and with lead acid batteries, achieving that 100% is so important for battery longevity and continued performance.
Lifepo4 batteries are different, and I defer to others on their proper recharging and implementation as I have no personal experience with them. In general they can charge faster, with less tapering as they approach full and can take advantage of a fast spinning cool alternator much much better than lead acid, and will not be damaged by not reaching full charge on every recharge cycle. They could very well wind up costing more initially, but be more reliable and longer lasting and Ultimately cheaper, than refining a charging system around maximizing the lifespan of lead acid batteries, which require that 100% recharge as often as possible.
